KR20200123488A - Doped and coated lithium transition metal oxide cathode materials for batteries in automotive applications - Google Patents

Abstract

The present invention provides a lithium metal oxide powder to be used as the cathode material of the rechargeable battery, the general formula _{Li 1 + d (Ni x Mn} y Co z Zr k M 'm) 1-d O 2 Li having a _{± e} A _f Consisting of metal oxide core particles, Al ₂ O ₃ is attached to the surface of the core particles, in the above formula 0 ≤ d ≤ 0.08, 0.2 ≤ x ≤ 0.9, 0 <y ≤ 0.7, 0 <z ≤ 0.4, 0 ≤ m ≤ 0.02, 0 <k ≤ 0.05, e <0.02, 0 ≤ f ≤ 0.02 and x + y + z + k + m = 1, M'is from groups Al, Mg, Ti, Cr, V, Fe and Ga Consists of one or more elements of the group F, P, C, Cl, S, Si, Ba, Y, Ca, B, Sn, Sb, Na and Zn, and Al in the powder _It relates to a lithium metal oxide powder having a ₂ O ₃ content of 0.05% to 1% by weight.

Description

Doped and coated lithium transition metal oxide cathode materials for automotive batteries {DOPED AND COATED LITHIUM TRANSITION METAL OXIDE CATHODE MATERIALS FOR BATTERIES IN AUTOMOTIVE APPLICATIONS}

The present invention relates to lithium transition metal oxides for use in rechargeable batteries doped and coated in a synergistic way to provide very good battery materials for demanding technologies such as the automotive field.

Rechargeable lithium and lithium ion batteries, due to their high energy density, can be used in a variety of mobile electronic device fields, such as mobile phones, laptop computers, digital cameras and video cameras. Commercially available lithium ion batteries are typically made of graphite-based anode and LiCoO ₂ -based cathode materials. However, LiCoO ₂ based cathode materials are expensive and typically have a relatively low capacity of around 150 mAh/g.

Alternatives to LiCoO ₂ based cathode materials include LNMCO class cathode materials. LNMCO stands for lithium-nickel-manganese-cobalt-oxides. The composition of LiMO ₂ or Li _{1 + x -} a _{'M 1 x'} O _2, where 'is a _m (which is referred to generally as "NMC" than, M, M = Ni _x Co _y Mn _z M is one or more dopants to be). LNMCO has a layered crystal structure similar to LiCoO ₂ (space group r-3m). The advantage of the LNMCO cathode is that the raw material cost of composition M is much cheaper compared to pure Co. The addition of Ni results in an increase in the discharge capacity, but this is limited by the decrease in thermal stability as the Ni content increases. In order to compensate for this problem, Mn is added as a structural stabilizing element, but at the same time some capacity is lost. A typical cathode material is the formula LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2 O 2, LiNi 0.6 Mn 0.2} Co 0.2 O 2 or Li _{1 .06} M _{0. 94} O comprising the composition having a _second, where _{M = Ni 1/3 Mn 1/3 Co 1/3} O 2 ( the latter Referred to as NMC111). The preparation of LNMCO is in most cases more complex than LiCoO ₂ because it requires a special precursor in which the transition metal cations are well mixed. Typical precursors are mixed transition metal hydroxides, oxyhydroxides or carbonates.

In the future, the lithium battery market is expected to be increasingly dominated by the automotive sector. The automotive sector is expensive and requires very large batteries that must be manufactured at the lowest possible cost. A significant part of the price comes from the cathode, ie the anode. Providing these electrodes in an inexpensive way can help reduce costs and increase market acceptance. Car batteries also need to last for years. During this time, the battery is not always running. Long battery life is related to two characteristics: (a) small reduction in capacity during storage and (b) high cycle stability.

The automotive market includes different major applications. Batteries for electric vehicles (EV) need to store energy for hundreds of kilometers of travel. Therefore, the battery is very large. Obviously, the required discharge rate does not exceed complete discharge within a few hours. Thus, a sufficient power density is easily achieved and no particular concern arises in dramatically improving the power performance of the battery. Cathode materials in such batteries need to have high capacity and good calender life.

In contrast, hybrid electric vehicles (HEVs) have much higher specific power requirements. Electric assisted acceleration and regenerative braking require the battery to be discharged or charged within seconds. At such high speeds, so-called direct current resistance (DCR) becomes important. DCR is measured by the appropriate pulse test of the battery. The measurement of DCR is described, for example, in "Appendix G, H, I and J of the USABC Electric Vehicle Battery Test Procedures", which can be found at http://www.uscar.org. USABC stands for "US advanced battery consortium" and USCAR stands for "United States Council for Automotive Research".

When the DCR resistance is small, then the charge-discharge cycle is very efficient; Only a small amount of ohmic heat is released. To achieve this high power requirement, the battery houses cells with thin electrodes. This allows (1) Li diffuses only over a short distance and (2) the current density (per electrode area) is small, contributing to high output and low DCR resistance. These high-power batteries impose stringent requirements on the cathode material: it should be able to maintain very high discharge or charge rates by contributing to the overall battery DCR as little as possible. In the past, this has been a problem with improving the DCR resistance of the cathode. Furthermore, it was a problem with limiting the increase in DCR during long-term operation of the battery.

The third type of vehicle battery is a battery for a plug-in hybrid electric vehicle (PHEV). The power requirement is less than that of the HEV, but higher than that of the EV type.

In the prior art, many methods are taught to improve the output characteristics as well as the battery life of the cathode material. However, in many cases these requirements contradict each other. As an example, it is quite generally accepted that reducing the particle size can increase the output of the cathode material with an increase in surface area. However, as one important contribution to limited battery life is the parasitary (undesired) side reaction that occurs between the charged cathode and the electrolyte at the particle/electrolyte interface, the increase in surface will have undesirable effects. I can. The rate of this reaction will increase as the surface area increases. Therefore, it is essential to develop a cathode material that has an improved output, particularly a low DCR, but does not further increase the surface area of the NMC cathode.

It has been widely reported how doping and coating can help improve the cycle stability of cathode materials and ultimately improve battery life. Unfortunately, many of these approaches lead to degradation in output capacity. In particular, doping with Zr, Mg, Al, etc., as well as coatings with phosphates, fluorites and oxides, have been reported, but in many cases and quite generally this leads to poor output performance. The inventors believe that this is associated with certain encapsulation effects that occur during doping or coating. Encapsulation prevents or limits the direct contact of the electrolyte with the filled LNMCO cathode surface, but at the same time makes it more difficult for lithium to penetrate the encapsulation layer. Therefore, it is essential to develop an improved treated cathode material that will improve battery life without causing a decrease in power.

Doping of the LNMCO material with Zr is known from US 8,343,662, wherein Zr is added to suppress a decrease in discharge voltage and capacity during a charge/discharge cycle and to improve cycle characteristics. Here, the Li precursor and the coprecipitated Ni-Mn-Co hydroxide are mixed with the Zr-oxide, and the mixture is heated at 1000°C in air.

In US 7,767,342, doping with oxides of "dissimilar" elements such as aluminum, silicon, titanium, vanadium and the like among lithium transition metal oxides to improve the storage properties of the battery by countering self-discharge and increased internal resistance. Is proposed. Expensive sintering methods have been proposed for Ni-Mn-Co composite oxides:

A) Mixing of Li-TM (transition metal)-oxides with oxides of elements "not equal to", and subsequent sintering,

B) mixing the Li- and TM-precursors with the “dissimilar” elemental precursors, and subsequently oxidizing the “dissimilar” elements by sintering in air and mixing them in the Li-TM-oxide; or

C) Mixing of Li-TM-oxide with a precursor of an element "not equal to", and subsequently sintering under oxidizing conditions.

One example of a prior art involving coating and subsequent heat treatment is US 8,007,941. There is disclosed a positive active material for a rechargeable lithium battery, which includes a core including at least one lithiated compound; And a surface treatment layer on the core forming an amphoteric active material, wherein the surface treatment layer comprises a coating material selected from the group consisting of non-lithium hydroxide or non-lithium oxyhydroxide, and the coating material is Sn, Ge, Ga, As, Zr, and a coating element selected from the group consisting of mixtures thereof, and the coating material is amorphous. The material is pretreated by heating to 400° C. to 600° C., followed by heating to 700° C. to 900° C. for 10 to 15 hours to remove carbon of the organic Al carrier.

Coatings with dopants selected from a long list including Zr and coatings with metal or metalloid oxides of LNMCO are both disclosed in US2011/0076556. However, there is no description as to why the dopant should be used, and the metal oxide may be one of a long list containing aluminum-, bismuth-, boron-, zirconium-magnesium-oxides (etc.). In addition, Al ₂ O ₃ coating is obtained by high temperature reaction of lithium metal oxide powder, resulting in precipitation of aluminum hydroxide. The additional heating step required after the wet precipitation step to obtain the aluminum oxide layer leads to an unfavorable situation in which the cathode and coating layer form an intermediate gradient.

US2002/0192148 discloses a method of forming a lithium metal anode protective layer for a lithium battery having a cathode, an electrolyte, and a lithium metal anode sequentially stacked with a lithium metal anode protective layer between the electrolyte and the lithium metal anode. The method includes activating the surface of a lithium metal anode; And forming a LiF protective layer on the activated surface of the lithium metal anode. In US2006/0275667, a composite oxide particle made of an oxide containing at least lithium (Li) and cobalt (Co); And a coating layer provided on at least a portion of the composite oxide particles and made of an oxide containing at least one of nickel and manganese and lithium. In US2005/0227147, lithium, nickel, and lithium nickel composite oxide containing at least one metal element other than lithium and nickel; And a layer containing lithium carbonate, aluminum hydroxide, and aluminum oxide, which is supported on a surface of the lithium nickel composite oxide. A positive electrode active material for a nonaqueous electrolyte secondary battery is disclosed.

It is an object of the present invention to provide an improved lithium transition metal cathode material for a positive electrode, which is manufactured in an inexpensive manner and is particularly suitable for the automotive battery field, particularly in view of the above-mentioned DCR and other problems.

Viewed from a first aspect the present invention provides a lithium metal oxide powder to be used as the cathode material of the rechargeable battery, the general formula _{Li 1 + d (Ni x Mn} y Co z Zr k M 'm) 1-d O 2 ± e It is composed of Li metal oxide core particles having A _f , and Al ₂ O ₃ is attached to the surface of the core particles, in the above formula 0 ≤ d ≤ 0.08, 0.2 ≤ x ≤ 0.9, 0 <y ≤ 0.7, 0 <z ≤ 0.4, 0 ≤ m ≤ 0.02, 0 <k ≤ 0.05, 0 ≤ e <0.02, 0 ≤ f ≤ 0.02 and x + y + z + k + m = 1, M'is the group Al, Mg, Ti, Cr , V, Fe and one or more elements from Ga, A is one or more elements from groups F, P, C, Cl, S, Si, Ba, Y, Ca, B, Sn, Sb, Na and Zn It is made of, and the Al ₂ O ₃ content of the powder can provide a lithium metal oxide powder of 0.05% by weight to 1% by weight. It is clear that embodiments where f = m = e = 0 can form part of the present invention. In one embodiment 0.002≦k≦0.02. In another embodiment, the Al ₂ O ₃ content in the powder is 0.1% to 0.5% by weight. One advantageous feature of the invention is that the concentration of Zr in the powder is higher at the surface than in the bulk of the Li metal oxide core particles. In yet another embodiment, the median particle size D50 of the core particles is between 2 μm and 5 μm. In large and dense particles, the rate-limiting properties are limited by the longer Li diffusion path within the particles. Thus, a large portion of the DCR resistance comes from bulk diffusion. In small particles, on the contrary, the Li diffusion path is shorter, and thus the bulk maintains a faster rate and thus DCR is more dominated by the surface charge transfer resistance. Therefore, the surface modification to lower the charge transfer resistance guarantees a large gain. We believe that the combination of alumina coating and Zr-dope provides the greatest benefit when the particles are small.

In various embodiments, Al ₂ O ₃ is attached to the surface of the core particles as a discontinuous coating. The attached Al ₂ O ₃ may be in the form of a plurality of individual particles with d50 <100 nm. In one embodiment, Al ₂ O ₃ is at least partially removably attached to the surface of the core particles by a dry coating method.

In other embodiments, 0 <xy <0.4 and 0.1 <z <0.4. In various embodiments, any one of x, y and z is 0.33±0.03, and 0.04 <d <0.08; x = 0.40±0.03, y = 0.30±0.03, z = 0.30±0.03, and 0.04 <d≦0.08; x = 0.50±0.03, y = 0.30±0.03, z = 0.20±0.03, and 0.02 <d <0.05; x = 0.60±0.03, y = 0.20±0.03, z = 0.20±0.03 and 0 <d <0.03. In general, one embodiment of the present invention may be 0.3 ≤ x ≤ 0.6, 0.2 <y <0.4, 0.2 <z <0.4 and 0 <d <0.08 or 0.2 <y <0.4, 0.2 ≤ z ≤ 0.4 and 0 ≤ d May be ≤ 0.08. This embodiment can be combined with another embodiment where 0.002≦k≦0.02 and the Al ₂ O ₃ content is 0.1% to 0.5% by weight.

It is apparent that further product embodiments according to the invention may be provided with the features covered by the different water embodiments described above.

As seen from the second aspect, the present invention is a method for producing a lithium metal oxide powder according to the present invention, wherein the powder is composed of Li metal oxide core particles and Al ₂ O ₃ attached to the surface of the core particles, and the method comprises

-Providing an Al ₂ O ₃ powder having a volume V1 and being a nanometer-sized non-aggregated powder;

-Providing a Li metal oxide core material having a volume V2; And

-Coating the Li metal oxide core material with Al ₂ O ₃ particles by mixing the Al ₂ O ₃ powder and the Li metal oxide core material by dry coating method

It can provide a manufacturing method comprising a. During the step of mixing the Al ₂ O ₃ powder and the Li metal oxide core material by dry coating method, the volume V1 + V2 = Va decreases until the volume remains constant at the value Vb, thereby reducing the Li metal oxide core material. Cover with Al ₂ O ₃ particles. This is a conventional method of providing the advantages of water according to the invention, which will become apparent in Comparative Example 1.

Viewing from the third aspect, the present invention will provide the use of the lithium metal oxide powder according to the invention in a mixture comprising a lithium metal oxide powder and another lithium transition metal oxide-based powder having a median particle size D50 greater than 5 μm. I can.

As viewed from the fourth aspect, the present invention can provide a battery including a cathode material including the lithium metal oxide powder according to the present invention, which is used in the automotive field.

In one embodiment, the battery is a battery of a hybrid electric vehicle.

Figure 1: SEM image of Al-coated + Zr-doped NMC433
Figure 2: Direct current resistance (DCR) measured by hybrid pulse power characterization (HPPC) at 25°C and different state of charge (SOC) for a series of NMC433 materials: pristine (P), Al-coated (Al), Zr-doped (Zr) and Al-coated + Zr-doped (Al + Zr).
Figure 3: Direct current resistance (DCR) measured by HPPC at -10°C and different state of charge (SOC) for NMC433 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al-coated + Zr-doped (Al + Zr)
Figure 4: Direct current resistance (DCR) measured by HPPC at 25° C. and different state of charge (SOC) for a series of NMC111 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al- Coating + Zr-Doping (Al + Zr)
Figure 5: Direct current resistance (DCR) measured by HPPC at -10°C and different state of charge (SOC) for a series of NMC111 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al -Coating + Zr-doped (Al + Zr)
Figure 6: Cycle life of 360 mAh battery at 4.2 V measured at 1C charge and discharge rate and 45°C for a series of NMC433 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al. -Coating + Zr-doped (Al + Zr)
Figure 7: Cycle life of 360 mAh battery at 4.2 V measured at 1C charge and discharge rate and 45°C for a series of NMC333 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al. -Coating + Zr-doped (Al + Zr)
Figure 8: Retention power (Q _ret ) measured monthly during storage tests at 60° C. on 360 mAh cells of a series of NMC433 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al-coated + Zr -Doping (Al + Zr) (m means month)
Figure 9: Recovery power (Q _rec ) measured monthly during storage tests at 60° C. on 360 mAh cells of a series of NMC433 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al-coated + Zr -Doping (Al + Zr) (m means month)
Figure 10: Increase in direct current resistance (DCR) measured monthly during storage tests at 60° C. on 360 mAh cells of a series of NMC433 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al-coated + Zr-doped (Al + Zr) (m means month)
Figure 11: Retention power (Q _ret ) measured monthly during storage tests at 60° C. on 360 mAh cells of a series of NMC111 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al-coated + Zr -Doping (Al + Zr) (m means month)
Figure 12: Recovery power (Q _rec ) measured monthly during storage tests at 60° C. on 360 mAh cells of a series of NMC111 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al-coated + Zr -Doping (Al + Zr) (m means month)
Figure 13: Increase in direct current resistance (DCR) measured monthly during storage tests at 60° C. on 360 mAh cells of a series of NMC111 materials: original (P), Al-coated (Al), Zr-doped (Zr) and Al-coated. + Zr-doped (Al + Zr) (m means month)
Figure 14: DC resistance (DCR) measured by HPPC at 25° C. and different state of charge (SOC) for NMC111: Al-coating + Zr-doped (-★-) vs. Zr-doped and Al-coated according to the invention And subsequent heat treatment (ㆍㆍ☆ㆍㆍ)
Figure 15: DC resistance (DCR) measured by HPPC at -10°C and different state of charge (SOC) for NMC111: Al-coating + Zr-doped (-★-) vs. Zr-doped and Al- according to the invention. Coating and subsequent heat treatment (ㆍㆍ☆ㆍㆍ)
Figure 16: Cycle life of 360 mAh battery at 4.2 V measured at 1C charge/discharge rate and 45°C for NMC333: Al-coating + Zr-doped (-★-) vs. Zr-doped and Al- according to the invention Coating and subsequent heat treatment (ㆍㆍ☆ㆍㆍ)
Figure 17: Retention power (Q _ret ) measured monthly during a storage test at 60° C. on a 360 mAh battery for NMC111: Al-coating according to the invention + Zr-doped (-★-) vs. Zr-doped and Al-coated and subsequent Heat treatment (ㆍㆍ☆ㆍㆍ)
Figure 18: Resilience (Q _rec ) measured monthly during a storage test at 60° C. on a 360 mAh battery for NMC111: Al-coating according to the invention + Zr-doped (-★-) vs. Zr-doped and Al-coated and subsequent Heat treatment (ㆍㆍ☆ㆍㆍ)
Figure 19: Increase in direct current resistance (DCR) measured monthly during a storage test at 60° C. on a 360 mAh battery for NMC111: Al-coating + Zr-doped (-★-) vs. Zr-doped and Al-coated according to the invention And subsequent heat treatment (ㆍㆍ☆ㆍㆍ)

The present invention provides a cathode material that has a lower DCR value and thus can be preferably applied as a cathode material for an HEV or PHEV battery. Of course its use as a cathode for traditional high power applications (eg power tools) is also within the scope of the invention. Furthermore, the cathode material of the present invention can be mixed with other cathode materials with a higher D50, which is the main goal to improve the output and DCR resistance of the latter, thereby fine-tuning the cathode mixture according to the desired end use. .

The present inventors have found a surprisingly synergistic effect when (1) doping an NMC-based cathode material with Zr and then (2) applying an Al ₂ O ₃ coating on the Zr-doped cathode material. Zr-doping can help to significantly improve the cycle stability of NMC-based cathode materials. This effect is at least partially related to the surface deformation.

Zr-doped Li metal oxide core particles can be prepared as follows:

(a) Precursors comprising Zr, eg ZrO ₂ , are mixed with lithium- and Ni-Mn-Co-precursors having the desired final NMC composition. The precursor is introduced into the container. The precursors are blended in a single-shaft mixer by dry powder mixing method,

(b) Sintering in an oxidizing atmosphere. The powder mixture from step (a) is sintered in a tunnel furnace in an oxidizing atmosphere. The sintering temperature is above 900° C. and the residence time is ˜10 hours. Dry air is used as oxidizing gas,

(c) After sintering, the sample is crushed in a mill to the desired particle size distribution.

The data indicated that the thermodynamic doping limit of Zr in the NMC cathode was very small. Thus, very small amounts of Zr are present in the bulk and there is an accumulation of excess Zr near the surface, possibly at the grain boundaries. The Zr probably protects the surface from excessive parasitic reactions with the electrolyte, and maybe the granular boundary is more robust against mechanical strain during fast cycling.

Furthermore, the inventors have found that the Al ₂ O ₃ nanoparticle coating on the NMC surface often has a mild positive effect of improving DCR and increasing cycle stability. NMC's Al ₂ O ₃ coating applies aluminum oxide nanoparticles to the surface of the cathode. It is not desirable for the cathode and coating layer to form an intermediate gradient, which is usually the case when heat treatment at higher temperatures is applied to the NMC-Al ₂ O ₃ composition. The gradient is achieved when some aluminum is chemically attached to the surface or diffuses into the outer part of the cathode, as in US 8,007,941 and US2011/0076556, and when some Li diffuses onto or within the aluminum to form LiAlO ₂ . On the contrary, it is advantageous for the Al ₂ O ₃ nanoparticles to be mechanically and removably attached to the surface, ie relatively loosely attached. The nanoparticles contribute to increasing the Brunauer-Emmett-Teller (BET) surface area of the cathode material without increasing the surface area of the NMC itself.

When applying the Al ₂ O ₃ nanoparticle coating to the surface of Zr-doped NMC, the present inventors have found a quite strong synergistic effect. The general properties (cycle stability and DCR output) in all cases were best compared to the Zr-doped (but not alumina coated) or alumina coated (but Zr-doped) reference. Furthermore, the resulting doped and coated material had much better properties than the expected additional results. In particular, Zr-doped without alumina coating resulted in less output than undoped NMC, while Zr-doped with alumina coating showed the best results, better than undoped and alumina coated NMC. In addition, the cycle stability of the Zr-doped and Al ₂ O ₃ coated cathodes was much better than expected compared to the Zr-doped or alumina coating only NMC. We can only guess why Al ₂ O ₃ so improves the DCR of Zr-doped NMC. The presence of a high surface area (alumina-) oxide on the surface-perhaps by dielectric properties-makes it possible to facilitate the charge transfer reaction.

The example will show results for a 3-4 μm LNMCO material. Small particle size cathodes were chosen to demonstrate how these known high power cathode materials can be further improved. While small particle particle LNMCO is a natural choice, embodiments of the invention are not limited to LNMCO with small particle size distribution (PSD). Embodiments of larger particle size LNMCOs with sufficiently large BET surface areas are within the scope of the present invention.

The examples also use cathode materials with a relatively high Li:M ratio. The value "x" for the lithium excess in Li _1+x M _1-x O ₂ is about 0.06 for NMC111. Li excess reduces cation mixing (i.e. Ni is located on the layered Li layer, which is a layered crystal structure) and thus supports high power-because Ni in the Li layer blocks the Li diffusion path. Cathode materials with excess Li “x” are a natural choice, but different embodiments of the invention are not limited to the specific Li excess value of x.

Further embodiment utilizes a transition metal composition is close to _{M = Ni 1/3 Mn 1} /3 Co 1/3 (NMC111) or _{M = Ni 0.38 Mn 0.29 Co 0.33} (NMC433). The composition is known to be "robust": because the Ni:Mn ratio is almost unity, the cathode has high air stability and relatively low soluble base content, and its preparation is simple. The concept of soluble base content is described for example in WO2012/107313. The relatively high Co content supports a good layered crystal structure, thereby ensuring high output power. Cathode materials having a high Co content as well as Ni:Mn of about 1 or slightly greater than this are a natural choice, but different embodiments of the invention are not limited to these Ni:Mn values and cobalt content.

Conclusion: In various embodiments the invention can be applied to a number of different sized particles with different Li:M stoichiometry and metal composition M. Illustrated NMC111 and x = 0.08 and M = Ni _{0 . 38} Mn _{0 . 29} Co _{0 .33} of 3-4 ㎛ L _{1+ x} M _{1 - x} O ₂ addition, the larger the particles, the less Co and higher Ni: a cathode having a Mn can be performed. For example, 5 μm LNMCO powder with cathode composition NMC = 532 and x = 0.03; Or an 8 μm LNMCO powder with cathode composition M = 622 and x = 0.01 is an embodiment of the present invention as long as the powder is Zr doped and coated with Al ₂ O ₃ nanoparticles.

The DCR test does not yield a single value, but its value is a function of the battery's state of charge (SOC). For LNMCO cathodes, the DCR increases at low charge states while flat or shows a minimum at high charge states. A high state of charge means a layered battery, and a low state of charge means a discharged battery. DCR is strongly dependent on temperature. Particularly at low temperatures, the cathode contribution to the DCR of the cell becomes dominant, so the low T measurement is quite selective to observe the improvement in DCR, which is directly responsible for the behavior of the cathode material. In the examples, the DCR results of the cathode of an actual full cell using the material according to the invention are reported. Typically the SOC varies between 20% and 90%, and the tests were carried out at representative temperatures of 25°C and -10°C.

Automotive batteries are expensive and therefore they are supported to last for years. The cathode material must meet stringent requirements. Here we will summarize these requirements as a "battery life" requirement, since battery life is not one simple characteristic. In real life, the battery is stored in different charging stages (during driving or stopping) and charging and discharging at different temperatures as well as at different voltages during operation. For development purposes, it is impossible to test cells for years under realistic conditions. To speed up the test, we apply the "accelerated life" test, which investigates different mechanisms contributing to a limited shelf-life.

Batteries are tested, for example at constant charge and discharge rates, to measure "cycle stability". Cycle stability can be tested under different voltage ranges, temperatures and current rates. Different mechanisms can be observed that can cause capacity loss under these different conditions. For example, slow cycling at high T shows mostly chemical stability, while fast cycling at low temperatures shows a dynamic behavior. The cycle stability results for the cathode-made according to the invention-in actual full cells are further reported. The test was carried out at a voltage range of 2.7-4.2 V, a temperature of 45° C. and a 1C charge-1C discharge rate.

The storage test examines the capacity loss after long storage (by measuring the residual amount or retention), and also the measured recovery after recharging. Additionally, the resistance is measured and compared to the initial value. The increase in resistance is an important result of damage to the battery during storage, as it directly affects the output capability. The DCR measurement is also a very sensitive tool for detecting (and inferring) to what extent undesirable side reactions have occurred (or will occur) in the cell during storage. To accelerate the test, storage is carried out at a high voltage (where the cell is initially fully charged at 4.2 V) and at a high temperature of 60° C., which accelerates undesirable side reactions. However, testing of capacity and DCR after storage is usually carried out at room temperature. The results of the storage test are additionally reported and represent the recovered capacity and retention measured at 25°C after storage at 60°C. The DCR measurement result after storage is also reported, and the graph will show the relative value compared to the DCR measurement before storage.

The particulate lithium transition metal oxide core material can be coated with alumina using a variety of coating processes. Alumina can be obtained by precipitation, spray drying, crushing, and the like. In one embodiment the alumina typically consists of primary particles having a BET of at least 50 m ² /g and d50 <100 nm, the primary particles being non-aggregated. In another embodiment, fumed alumina or surface treated fumed alumina is used. Fumed alumina nanoparticles are made in a high temperature hydrogen-air flame and are used in a number of applications involving everyday use products. The crystalline structure of fumed alumina is maintained during the coating process and is thus found in the coating layer surrounding the LiMO ₂ core. This latter method is the easiest and cheapest way to apply alumina particles onto an NMC core.

The invention will now be illustrated in the following examples:

Example 1:

This example demonstrates that the Al-coated + Zr-doped NMC433 cathode material yields the best output performance compared to the original, Al-coated only and Zr-doped materials. NMC 433 means Li _1.08 M _0.92 O ₂ , and M = Ni _0.38 Mn _0.29 Co _0.33 O ₂ .

NMC 433 Preparation: Doped and coated NMC433 was prepared on a pilot line of Yumicore (Korea) by the following steps: (a) blending of lithium and nickel-manganese-cobalt precursors and Zr oxide; (b) synthesis in an oxidizing atmosphere; (c) crushing and (d) alumina dry coating. A detailed description of each step is as follows:

Step (a): Blending of ZrO ₂ , lithium- and Ni-Mn-Co- precursors with the desired final 433 composition using a dry powder mixing method, targeting a molar ratio to ZrO ₂ of 1 mol%. The precursor is introduced into the container. ZrO ₂ particles were tetragonal and monoclinic phase, had an average primary particle size of 12 nm and a BET of 60 ± 15 m ² /g. They were mixed with lithium carbonate, a precursor of lithium and Ni-Mn-Co, and mixed Ni-Mn-Co oxyhydroxide. The precursors were blended in a vertical single axis mixer by dry powder mixing method.

Step (b): Sintering in an oxidizing atmosphere. The powder mixture from step (a) was sintered in a tunnel furnace in an oxidizing atmosphere. The sintering temperature was above 900° C. and the residence time was -10 hours. Dry air was used as the oxidizing gas.

Step (c): After sintering, the sample was crushed in a grinder to a particle size distribution with D50 = 3-4 μm. The span was 1.20. Span is defined as (D90-D10)/D50, where DXX is the corresponding XX value of the volume distribution of the particle size analysis.

Step (d): 1 kg of NMC433 was charged into a mixer (for example, a 2L Hanschel type mixer) and 2 g of fumed alumina (Al ₂ O ₃ ) nanopowder was added. During mixing at 1000 rpm for 30 minutes, the fumed alumina slowly disappeared from the field of view, yielding a coated NMC powder that looked very similar to the initial powder. With this quantitative ratio of precursor/fumed alumina, an aluminum coating level of 0.3625 mol% was achieved (this corresponds to 0.1 wt% aluminum or about 0.2 wt% alumina). Further analysis indicates that the alumina is loosely or removably attached to the surface, and a significant portion of the alumina particles can actually be separated from the core by suitable washing with water.

1 shows an SEM image of an Al-coated + Zr-doped NMC 433 according to the present invention. The lithium metal oxide powder consists of agglomerated submicron-sized microcrystals. The presence of individual particles of alumina (or nanometer-sized islands) on the surface is evident.

Slurry preparation and coating

A slurry was prepared by mixing NMC 433 doped and coated with 700 g of NMP, 47.19 g of super P® (conductive carbon black manufactured by Timcal) and 393.26 g of a 10% by weight PVDF binder in an NMP solution. The mixture was mixed for 2.5 hours in a planetary mixer. Additional NMP was added during mixing. The mixture was transferred to a Disper mixer and mixed for 1.5 hours under the addition of additional NMP. The typical total amount of NMP used was 423.57 g. The final solids content in the slurry was about 65% by weight. The slurry was transferred to the coating line. A double coated electrode was prepared. The electrode surface was smooth. The electrode loading was 9.6 mg/cm ² . The electrode was pressed with a roll press to achieve an electrode density of about 3.2 g/cm ³ . A pouch cell type complete cell was prepared as described below using the electrode.

Full battery assembly

For the purpose of full cell testing, the prepared positive electrode (cathode) was assembled with a negative electrode (anode), which is usually graphite type carbon, and a porous electrical insulating film (separator). Complete cells were prepared by the following main steps: (a) electrode slitting, (b) electrode drying, (c) jelly roll winding, and (d) packaging.

(a) Electrode slitting: After NMP coating, the electrode active material may be slitting by a slitting machine. The width and length of the electrode is determined by the battery application.

(b) Attachment of tabs: There are two types of tabs. The aluminum tab is attached to the anode (cathode), and the copper tab is attached to the cathode (anode).

(c) Electrode drying: The prepared positive electrode (cathode) and negative electrode (anode) were dried at 85° C. to 120° C. for 8 hours in a vacuum oven.

(d) Jelly roll winding: After drying the electrode, a jelly roll was prepared using a winding machine. The jelly roll consists of at least a negative electrode (anode), a porous electrical insulating film (separator), and a positive electrode (cathode).

(e) Packaging: The prepared jelly roll was introduced into a 360 mAh battery having an aluminum laminate film package to yield a pouch battery. Additionally, jelly roll was impregnated with electrolyte. The amount of electrolyte was calculated according to the porosity and dimensions of the positive and negative electrodes, and the porous separator. Finally the packaged complete cell was sealed by a sealer.

The DCR resistance was obtained from the voltage response to the current pulse, and the process used was in accordance with the USABC standard mentioned above. DCR resistance is very relevant to practical application because data is used to estimate the fade rate so that battery life can be predicted in the future, furthermore, DCR resistance is very useful for detecting damage to electrodes. It is sensitive because the reaction product of the reaction between the electrolyte and the anode or cathode precipitates as a low-conductivity surface layer.

The process is as follows: Using a test profile that introduces a 10 second charge and a 10 second discharge pulse at each 10% state of charge (SOC) step, the cell is tested by HPPC to provide dynamic power over the available voltage range of the device. Was determined. In the present invention, the HPPC test was performed at both 25°C and -10°C. The test process for a 25° C. HPPC is as follows: first charge the cell between 2.7 V and 4.2 V under CC/CV (constant current/constant voltage) mode at a rate of 1 C (corresponding to the current discharging the charged cell within 1 hour)- Discharge-charged. The cell is then discharged under CC mode at a rate of 1 C at 90% SOC, where a 10 second discharge is applied at a rate of 6 C (corresponding to the current discharging the charged cell in 1/6 hour) followed by 10 at a rate of 4 C. Charged in seconds. Discharge and charge DC resistance (DCR) was calculated at 90% SOC using the difference in voltage during pulse discharge and pulse charging. The cells were then discharged stepwise at different SOCs (80%-20%) at a rate of 1C, and at each SOC, the 10s HPPC test was repeated as described above. The HPPC test at -10°C was basically the same as the test at 25°C, except that a 10 second discharge pulse was performed at a rate of 2C and a 10 second charge pulse was performed at a rate of 1C. In order to avoid the effect of self-heating of the battery on the battery temperature during charging and discharging, a fixed relaxation time was applied after each charging and discharging step. HPPC tests were performed on two cells of each cathode material at each temperature and the DCR results were averaged for the two cells and plotted against SOC. Basically, lower DCR corresponded to higher output performance.

Figure 2 shows the DCR results of a series of NMC433 cells measured at 25° C.: original, Al-coated, Zr-doped and Al-coated + Zr-doped. Compared to the original, the Al-coated cathode yields a smaller DCR over the entire SOC range, thus obtaining a better output performance. Zr-doped cathodes generally lead to higher DCR. Therefore, the output performance is inferior to the original. However, surprisingly, the combination of Al-coating and Zr-doping provides the best DCR and power performance. 3 shows the DCR results of the same series of NMC433 cells measured at -10°C. Although the Al-coated only and Zr-doped only materials exhibit higher DCR values than the original material, surprisingly, the Al-coated + Zr-doped material still provides the best DCR and power performance of all materials.

Example 2:

In this example, the NMC111 material was prepared using the same method as in Example 1 and incorporated into a full cell. Powder has a D50 of 3-4 ㎛ and 1.13 Li / M ratio (corresponding to _{Li 1 .06 M 0. 94 O 2} ). The content of Zr and Al is also the same: 1 mol% ZrO ₂ and 0.2 wt% alumina. This example confirms the same effect as observed in Example 1 on the cathode material NMC111: the combination of Al-coating and Zr-doping is the lowest DCR and thus the original, Al-coating only or Zr-doped only. It yields the best output performance compared to the material. HPPC test conditions are as described in Example 1, and DCR results at 25°C and -10°C are shown in FIGS. 4 and 5, respectively.

Example 3:

This example demonstrates that the Al-coated + Zr-doped NMC433 cathode material of Example 1 yields the best cycle life at 45° C. compared to the original, Al-coated only and Zr-doped materials. . For a positive cathode material used in an electric vehicle that will probably be charged and discharged more than 1,000 times, it is very important to have a long cycle life corresponding to good cycle stability. To estimate the cycle life of the cathode material in a short period in the laboratory, a 360 mAh pouch cell was cycled between 2.7 V and 4.2 V at both charge and discharge rates of 1 C. CC/CV mode was applied during charging and CC mode was used during discharging. To simulate the harshest conditions, cycling was performed in a 45° C. chamber and cells were differentiated. Both differences in cathode material and cell variations during manufacture could lead to differences in pouch cell capacity. All cell capacities were normalized to the discharge capacity of the second cycle QD2.

A plot of cycle life is shown in FIG. 6. The cycle life of the original was the worst of the series. The Al-coated only material slightly improved the cycle life, and the Zr-doped only material further improved the cycle life. The combination of Al-coated and Zr-doped yielded the best cycle life, which was an unpredictable result based on the results of Zr-doped and Al-coated materials.

Example 4:

This example corroborates the results in the cathode material NMC111 of Example 2, which is the same as observed in Example 3: The combination of Al-coating and Zr-doped original, Al-coated only and Zr-doped only materials. The best cycle life was induced at 45° C. compared to (same test as in Example 3). The cycle life test conditions were all the same as those described in Example 3. As shown in Fig. 7, the cycle life of the original was the worst among the series of materials. Both Al-coating and Zr-doped improved the cycle life of NMC111. The best and most unexpected improvement came from the combination of both Al-coating and Zr-doped.

Example 5:

This example shows that the Al-coated + Zr-doped NMC433 cathode material of Example 1 is the best holding power, the best resilience, and the best during the storage test at 60° C. compared to the original, Al-coating only and Zr-doped materials. Small = demonstrates that it yields the best DCR increase.

For positive cathode materials used in electric vehicles that are expected to last as long as similar gasoline powered vehicles, having a long calender life is crucial. In order to investigate the calendar life behavior and to be able to differentiate cells within a short test period, 360 mAh cells were stored at 60° C. in the chamber for 3 months. After every 1 month of storage, the cells were removed from the chamber and the holding power was checked. Thereafter, the battery was first discharged to 2.7 V under CC mode and then charged to 4.2 V to confirm the resilience. DCR was also measured at 3 V during discharge. For a fair comparison between different cells, all measured capacity and DCR data were normalized for initial capacity and initial DCR.

8 shows a normalized retention (Q _ret ) plot of a 360 mAh cell made from a series of NMC433 materials. The holding power of the original material rapidly decreased over time. Materials with only Al-coating did not improve performance and even worsened after 2 months. Materials with only Zr-dope have improved retention. And surprisingly, the combination of Al-coating + Zr-doped further improved this. 9 shows the effect of Al-coating + Zr-doping on the recovery power (Q _rec ) in the storage test. This tendency is the same for holding power. In FIG. 10, normalized DCR values versus time are plotted. DCR increased rapidly during storage, especially for raw and Al-coated materials only. The Zr-doped only material slowed the rate of DCR increase, but the Al-coated + Zr-doped material further improved it. In summary, the combination of Al-coating and Zr-doped yielded the best performance during storage tests at 60°C.

Example 6:

This example confirms the same effect in the cathode material NMC111 of Example 2 as observed in Example 5: The combination of Al-coating and Zr-doped original, Al-coated only and Zr-doped only materials. Compared to the storage test at 60° C., it provided the best retention (FIG. 11 ), the best recovery (FIG. 12 ), and the best DCR increase (FIG. 13 ). Temperature storage test conditions were the same as those described in Example 5.

Control Example 1:

In this control example, 1 mol% Zr-doped NMC111 was dry coated with 0.2 wt% Al ₂ O ₃ nanoparticles and then heat treated at an intermediate temperature of 375°C. A gradient was achieved as some aluminum was chemically attached to the surface and/or diffused to the outer portion of the core of the cathode powder, and some Li diffused onto and/or within the alumina coating to form LiAlO ₂ . Its chemical performance was compared with the performance of Al dry coating + Zr-doped material in FIGS. 14 to 19, which shows that Al dry coating is DCR at room temperature (FIG. 14) and low temperature (-10°C, FIG. 15) (Example Measurement as in 1-2), cycle life at 45° C. (measurement as in FIG. 16, Example 3-4), holding power (FIG. 17), resilience (FIG. 18) and DCR increase during storage at 60° C. 19) (Measurement as in Example 5-6) showed superiority to Al gradient coating. In each of Figs. 14 to 19, -★- refers to the powder according to the present invention, and ㆍ·☆·· refers to the powder of the control example. Since the heating temperature in US2011/0076556 is higher than that of this control example, the diffusion of Al and Li will be more certain, and the full cell test results for this material will not be much better than the results of control example 1.

While specific embodiments and/or detailed descriptions of the present invention have been shown and described above to illustrate the application of the principles of the present invention, the present invention is described more fully in the following claims, or as otherwise known to those skilled in the art. It will be understood that together (including all equivalents) are included without departing from these principles.

Claims (16)

A lithium metal oxide powder to be used as the cathode material of the rechargeable battery, the general formula Li _{1 + d} (Ni _x Mn _y Co _z Zr _k M _'m) Li metal oxide core particles having a _{1-d O 2 ± e A} f And Al ₂ O ₃ is attached to the surface of the core particles, in the above formula 0 ≤ d ≤ 0.08, 0.2 ≤ x ≤ 0.9, 0 <y ≤ 0.7, 0 <z ≤ 0.4, 0 ≤ m ≤ 0.02, 0 <k ≤ 0.05, 0 ≤ e <0.02, 0 ≤ f ≤ 0.02 and x + y + z + k + m = 1, M'is one from the groups Al, Mg, Ti, Cr, V, Fe and Ga Consists of the above elements, A consists of one or more elements from groups F, P, C, Cl, S, Si, Ba, Y, Ca, B, Sn, Sb, Na and Zn, and Al ₂ O in the powder ₃ Lithium metal oxide powder having a content of 0.05% by weight to 1% by weight. The lithium metal oxide powder according to claim 1, wherein the core particle has a median particle size D50 of 2 µm to 5 µm. The lithium metal oxide powder according to claim 1, wherein Al ₂ O ₃ is attached to the surface of the core particles as a discontinuous coating. The lithium metal oxide powder of claim 1, wherein Al ₂ O ₃ is attached to the surface of the core particles in the form of a plurality of individual particles having d50 <100 nm. The lithium metal oxide powder according to claim 1, wherein Al ₂ O ₃ is detachably attached to the surface of the core particles by a dry coating method. The lithium metal oxide powder according to claim 1, wherein 0 <x-y <0.4 and 0.1 <z <0.4. The lithium metal oxide powder of claim 1, wherein each of x, y and z is 0.33±0.03, and 0.04 <d <0.08. The lithium metal oxide powder according to claim 1, wherein x = 0.40 ± 0.03, y = 0.30 ± 0.03, z = 0.30 ± 0.03 and 0.04 <d ≤ 0.08. The lithium metal oxide powder according to claim 1, wherein x = 0.50 ± 0.03, y = 0.30 ± 0.03, z = 0.20 ± 0.03 and 0.02 <d <0.05. The lithium metal oxide powder according to claim 1, wherein x = 0.60 ± 0.03, y = 0.20 ± 0.03, z = 0.20 ± 0.03 and 0 <d <0.03. The lithium metal oxide powder of claim 1, wherein the concentration of Zr is higher at the surface than in the bulk of the Li metal oxide core particles. A method for producing a lithium metal oxide powder according to any one of claims 1 to 11, wherein the powder comprises Li metal oxide core particles and Al ₂ O ₃ attached to the surface of the core particles, and the method comprises:
-Providing an Al ₂ O ₃ powder having a volume V1 and being a nanometer-sized non-aggregated powder;
-Providing a Li metal oxide core material having a volume V2; And
-Coating the Li metal oxide core material with Al ₂ O ₃ particles by mixing the Al ₂ O ₃ powder and the Li metal oxide core material by dry coating method
Manufacturing method comprising a. The method of claim 12, wherein during the step of mixing the Al ₂ O ₃ powder and the Li metal oxide core material by a dry coating method, the volume V1 + V2 = Va decreases until the volume remains constant at the value Vb, whereby Li metal oxide core material is coated with Al ₂ O ₃ particles. Use of the lithium metal oxide powder according to any one of claims 1 to 11 in a mixture comprising a lithium metal oxide powder and another lithium transition metal oxide-based powder having a median particle size D50 greater than 5 μm. A battery comprising a cathode material comprising the lithium metal oxide powder according to any one of claims 1 to 11, which is used in an automobile field. A battery of a hybrid electric vehicle comprising a cathode material containing the lithium metal oxide powder of any one of claims 1 to 11.

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